Voice transmitting gas mask



March 29, 1955 P. M. WORKINGER 2,705,052 VOICE TRANSMITTING GAS MASK Filed Dec. 17. 1951 2 ShBQtS-ShGGt 1 Paul M. War/zinger INVENTOR.

P. M. WORKINGER VOICE TRANSMITTING GAS MASK March 29, 1955 I 2 Sheets-Sheet 2 Filed Dec. 17, 1951 Paul M. Workinger- INVENTOR. BY Q...

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United States Patent VOICE TRANSMITTING GAS MASK Paul M. Workinger, Edgewood, Md. Application December 17, 1951, Serial No. 262,105

4 Claims. (Cl. 181-18) This invention relates to voice transmitting gas masks and other breathing apparatus, including a face piece tightly covering the entire face of the wearer of the gas mask or a substantial portion thereof, including the mouth and nose, and it has for its general object to provide improved means for the transmission of the wearers voice, enabling the wearer of the mask to make himself heard to the extent that the speech may be understood without undue effort in speaking. 7

Certain difficulties are experienced in connection with the transmission of voice through a gas mask or through another face covering breathing apparatus. It is inadvis- 1 able to use speaking apparatus operated electrically, because dry cell batteries and the like remain operative only through a very limited time and constant renewal of the batteries also during periods f0 non-use of the gas mask would be necessary to keep the gas mask or a breathing apparatus in good condition for an emergency. Moreover, the battery cannot be held by the gas mask itself and thus constitutes a second unit which must be worn by the wearer of the gas mask.

Voice transmission through the usual type of metallic diaphragm which is not excited electromagnetically has however its difficulties as the diaphragm must be responsive to a wide range of voice frequencies to reproduce voice with suflicient fidelity for intelligible and effortless communication. The natural oscillation frequency of metallic diaphragms, selected within the frequency range to be covered or close to the limits of this range, interferes with intelligible speech on account of the preference accorded to the reproduction of certain frequencies. If however the natural frequency of a metallic diaphragm is entirely outside the frequency range of the human voice the energy necessary to move the diaphragm 18 at the highest level. As the energy produced by the human voice is very low it is necessary to use light weight diaphragrns which are movable by the low vo1ce energy. This condition is however at variance with the condition imposed on the diaphragm to be impervious to gas which condition requires a minimum thickness. Therefore a direct transmission merely by means of a diaphragm is usually not feasible and other expedients, such as acoustical chambers associated with the diaphragm and the like have been recommended which however produce a complication of the gas mask construction.

It has been found by experiment that a satisfactory voice reproduction under the circumstances which have been described above can be obtained with thin rubber diaphragms or membranes closing tightly a speaking tube inserted into the face piece of the gas mask which membranes must be resiliently held at the rim of the speaking tube.

Such diaphragms do not have a natural oscillation frequency which they tend to adopt and moreover they are impervious to gases even when of very moderatethickness and they make large excursions even when drlven with low energy. The kinetic energy of the membrane, returning from an excursion, which has to be overcome at each cycle is very low so that the Weight of such a diaphragm is not limited to the same extent as 1n other rigid diaphragms such as the metallic diaphragm. Further sounds may partly pass through a rubber diaphragm member and this passage may even be promoted by a suitable fixation of the membrane.

It has been found that large excursions of the membrane are possible with two modes of holding the rubber diaphragm or membrane one mode permitting to hold the marginal portion of the membrane more rigidly and another mode which gives the most perfect results and in which the diaphragm is not held positively along the margin of the opening but is held along a cylindrical part of the tube which it closes by means of an elastic band or cord.

The invention is illustrated in the accompanying drawing showing two embodiments thereof. It is however to be understood that the embodiments shown do not represent the sole embodiments of the invention which are hereinafter described and that the illustrated embodiments therefore are only examples intended to facilitate the explanation of the principle of the invention and the best mode of applying said principle. A departure from the examples which have been illustrated does therefore not necessarily involve a departure from the principle of the invention.

In the drawing:

Figure 1 is a perspective view of a gas mask.

Figure 2 is a perspective fragmentary view on a larger scale of the speaking tube seen from the front.

Figure 3 is an elevational sectional view through part of the gas mask carrying the speaking and voice transmission device.

Figure 4 is an elevational sectional fragmentary view of a second embodiment of the voice transmission device.

Figure 5 is a perspective fragmentary view of the embodiment of the voice transmission device shown in Figure 4 with the rubber membrane removed.

Figure 6 is an exploded perspective and sectional view of ctihe speaking tube and membrane illustrated in Figure 3, an

Figure 7 is a perspective view of the membrane as used in the modification illustrated in Figure 4.

Figure 1 illustrates a gas mask 10 of conventional design which is provided with the customary face mask piece 11 of a flexible and impervious material which is provided with the customary head straps 12 and with openings which are surrounded by the eye pieces or lenses 15. On a lateral part of the lower section of the gas mask a tubular fitting 16 is arranged to which a flexible air hose 14 is attached which leads to the customary canister (not shown). On the lower portion of the face piece of the mask an exiaation opening with an exhalation valve 17 is pro- Vl e Above the exhalation opening and preferably facing the region occupied by the mouth of the wearer of the gas mask a speaking tube 20 is mounted which forms the voice transmission device and which is preferably seated on or within a flange or sleeve-like projection 21 surrounding a tubular trunk piece 23 slightly projecting from the face mask piece which surrounds the speaking opening 22. On the outside the speaking tube may be surrounded With a sound guiding megaphone tube 24, However the use of the megaphone tube is optional and it does not form a necessary accessory.

The speaking tube holds the speaking membrane and two different modifications of this membrane have been shown in the figures.

In the modification shown in Figure 3 the speaking tube 20 is provided with a threaded flange 25 projecting outwardly from the tube over which a cap 28 may be screwed by means of internal screw threads 27 provided on the same. The flange 25 ends in a flat surface 33 while the cap 28 is provided with an inwardly projecting flange 34 facing this flat surface. Between the surface 33 and the inwardly projecting flange 34 the membrane 30 may be held. The membrane consists entirely of rubber and comprises a central and thin flat portion 36 and an outer, reinforced and thicker annular flange or rim portion 38. This thicker rim portion 38 is clamped between the surface 33 of the flange 25 and the inwardly projecting flange 34. As the membrane 30 is entirely made of thin rubber a clamping of the outer annular flange portion 38 does not prevent the inner portion 36 from moving freely making relatively large excursions.

Partly the sound produced by the wearer of the gas mask traverses the rubber and thus penetrates directly to the outside but partly the pressure increases on the inside and produces a vibration of the membrane. The

opening 22 of the face piece 11 remains tightly closed on account of the tight holding of the annular flange 38 of the membrane 30 between the two members 25 and 28 of the speaking tube.

The tubular trunk piece 23 of the face piece 11 of the gas mask may hold an angle tube 20a as shown in Figure 4 with an inner cylindrical face which is seated on the outwardly projecting flange 21 of the trunk piece 23. The rear edge of the angle tube 20a may be bent inwardly and it thus surrounds the flange 21 of the trunk piece 23 on its periphery and covers its back. The front edge of the angle tube 20a may also be bent inwardly and may be rounded. This angle tube is provided with a small groove 42 in its cylindrical section which groove is arranged at some distance from the front opening of the angle tube 20a. A membrane 50 consisting merely of a piece of thin rubber is fastened over the front opening and also covers part of the peripheral cylindrical portion over which it is fitted snugly and it is fastened on the angle tube 20a by means of an elastic band or cord which by virtue of its elasticity snaps into the groove on top of the membrane. The elastic band or cord fact somewhat smaller than the perip ery of the speaking tube so that when held in the groove the band or cord is under elastic tension.

This elastic band 44 may also be cemented or otherwise held on the outer portion of the membrane as shown in Figure 7.

When the elastic band 44 holds the membrane 50 in the groove 42 the said membrane is tensioned so that it is held stretched in front of the opening of the angle tube 20a. The angle tube 20a is held in the trunk piece 23 by holding and sound guiding member 24 which fits snugly over the angle tube 20a so that the latter is firmly clamped between the holding and sound guiding tube 24 and the flange 21 of the trunk piece 23. The holding and sound guiding member 24 may be provided at one of its ends with an inwardly turned flange fitting over and gripping the back portion of the angle tube 20a.

As above stated the angle tube 20a has its front portion covered by the membrane 50 and this portion fits snugly into the holding and sound guiding tube 24 which therefore not only holds the angle tube and membrane but which also projects beyond the membrane. This projecting portion has a flaring inside which serves as a horn or megaphone. The membrane then closes tightly the front opening of the speaking tube and it may also vibrate when sounds are produced on the inside. The excursions of the membrane find less resistance when the membrane is held in the manner shown in Figure 4 because the point of fixation is in this case located between the rim of the angle tube and the holding and sound guiding tube and the membrane is held along a cylindrical surface rather than in the manner shown in the modification illustrated in Figures 3 and 6. Moreover the membrane is held on the rounded inwardly bent end of the angle tube 20a and it is pressed against the rounded end of the angle tube only on one of its sides.

The angle tube 20a, if properly mounted, is held on the flange 21 of the trunk piece 23 between the groove 42, which produces a protruding ridge on the inside of the angle tube, and the bent flange of the same, thus securing a firm and stable seating of the angle tube.

The tubular trunk piece 23 of the face piece 11 of the mask may hold a wire mesh plate or disk 40 which is provided for the purpose of preventing the membrane fronii being drawn inwardly during the testing of the gas mas 4 Preferably the rubber membrane has a thickness varying between .002 inch to .030 inch. As such a membrane will deteriorate in the course of a long time it will be necessary to mark it by color, by a date stamp, or the like in order to facilitate the locating of membranes which are must be so dimensioned that its peri heral length is in due for replacement on account of age, climatic conditions or other reasons.

The described construction of a rubber membrane and especially the use of a membrane in the manner illustrated in Figures 4 and 5 of the drawings according to which the membrane is fixed on the cylindrical part of the speaking tube near the front end and held there by an elastic band or cord has been found to be superior to other membrane constructions mainly by experimentation which showed that the transmission of sound was much clearer and more intelligible with membranes of the above mentioned type and was much preferable to constructions in which a rigid membrane, such as a metal membrane, or another membrane of rigid material was used. Among various means of fixation of the membrane the fixation by means of an elastic band was found to produce the best results.

It will be clear that nonessential parts of the construction as above shown may be changed without in any way departing from the essence of the invention as defined in the annexed claims.

Having described the invention, what is claimed as new 1s:

1. A voice transmitting gas mask with a face piece tightly fitting over the face of the wearer, comprising a speech transmission unit mounted on a trunk piece surrounding an opening of the face piece, said unit including an angle tube provided with a-groove, firmly seated on and surrounding said trunk piece, a membrane covering the cylindrical portion of the angle tube in front of the groove and the frontal cross-section of the angle tube, a holding and sound guiding tube with a cylindrical inner surface fitting snugly over the angle tube and projecting on the front side beyond the angle tube and the membrane, the inner surface of the projecting portion of the holding and sound guiding tube being flared to act as a sound amplifier, and elastic means on said membrane for holding the end of the membrane tightly within the groove of the angle tube, while the adjacent portion of the membrane is clamped between the cylindrical portion of the angle tube and the holding and sound guiding tube surrounding it.

2. A voice transmitting gas mask as claimed in claim 1, wherein the front end of the angle tube is rounded and the rubber membrane covers the opening, the rounded end portion and a cylindrical portion and is stretched over the end portion by elastic means pressing on its marginal portion forcing it into the groove.

3. A voice transmitting gas mask as claimed in claim 1, wherein the elastic means comprises an elastic band fixedly carried by the edge of the rubber membrane, and contracting the same, so that said edge is normally contracted when the rubber membrane is not mounted on the speaking tube and is held under elastic tension when mounted on the speaking tube.

4. A voice transmitting gas mask as claimed in claim 1, wherein the speaking opening is provided with a wire mesh for preventing the rubber membrane from being stretched beyond a predetermined limit during tests.

References Cited in the file of this patent UNITED STATES PATENTS 1,329,430 Pollard Feb. 3, 1920 1,406,425 Stair Feb. 14, 1922 1,410,034 Pollard Mar. 21, 1922 2,038,267 Bullard Apr. 21, 1936 2,300,912 Dodge et al. Nov. 3, 1942 2,326,650 Husted Aug. 10, 1943 2,410,454 Hotsinger Nov. 5, 1946 FOREIGN PATENTS 566,098 Great Britain Dec. 13, 1944 

